iv THE SENSE OF SMELL 181 



speaking, cases of partial congenital anosmia are rare ; but it may 

 be doubted whether they are so in reality, or whether the absence 

 of smell for certain odours has not been overlooked or left un- 

 diagnosed, and only discovered accidentally. The English chemist 

 D. H. Nagel was unable to perceive the specific odour of cyanic 

 acid, which resembles that of bitter almonds, and found the same 

 in several of his students, though their smell was normal for all 

 other odours. 



Cases of partial anosmia after illness are more frequent. 

 Zwaardemaker draws attention to the alterations of smell after 

 diphtheria and influenza ; in certain cases, which he investigated, 

 the anosmia does not extend to all odours. Sensibility to certain 

 smells appears to be abolished, to others it is merely weakened, 

 to others unchanged. Winkler in his neurological clinic observed 

 a tabetic who exhibited almost complete anosmia for the smell of 

 benzoin, though he recognised the smell of musk. In the same 

 clinic another patient could not smell musk, but perceived benzoin 

 better than other odours. 



Parosmia, and subjective or hallucinatory smells also have a 

 certain importance in regard to the question of the specific 

 olfactory energies. 



Joh. Miiller describes a patient who constantly complained of 

 bad smells, and the post-mortem examination showed that the 

 arachnoid had ossified in several places, and there were areas of 

 softening in the cerebral hemispheres. A. Dubois knew a man 

 who after a fall from his horse had for many years till his death 

 the sensation of a foetid odour. Many physicians have observed 

 patients who had a constant sensation of a smell of burning, 

 similar to that produced by lighting wooden matches. Other 

 patients complain of a persistent smell of faecal odours. It is 

 important to note that these hallucinatory sensations are perceived 

 most distinctly during the inspiratory act and on sniffing, as if 

 the activity of the perceptive centre was aroused by the olfactory 

 substances introduced with the air to the peripheral organ. We 

 may exclude Lud wig's suggestion that the subjective sensation of 

 faecal odours in some patients depends on reabsorption into the 

 blood of the products of intestinal putrefaction, which directly 

 excite the olfactory centre. Zwaardemaker proved, in fact, that 

 olfactory hallucinations may be associated with complete objective 

 anosmia to the odours perceived subjectively. 



Generally speaking, olfactory hallucinations are rare. Smell is 

 seldom represented in dreams (Brillat-Savarin, De Sanctis, Kiesow 

 and others), although the two last believe it is more common than is 

 generally supposed. This agrees with the fact that it is difficult, 

 even by a strong effort of will, to evoke memory images of the 

 commonest smells, as we can easily recall visual, and particularly 

 acoustic and musical, sensations. But that in certain cases 



